Polybenzimidazole compounds, polymeric media, and methods of post-polymerization modifications

ABSTRACT

A PBI compound includes imidazole nitrogens at least a portion of which are substituted with a moiety containing a carbonyl group, the substituted imidazole nitrogens being bonded to carbon of the carbonyl group. At least 85% of the nitrogens may be substituted. The carbonyl-containing moiety may include RCO—, where R is alkoxy or haloalkyl. The PBI compound may exhibit a first temperature marking an onset of weight loss corresponding to reversion of the substituted PBI that is less than a second temperature marking an onset of decomposition of an otherwise identical PBI compound without the substituted moiety. The PBI compound may be included in separatory media. A substituted PBI synthesis method may include providing a parent PBI in a less than 5 wt % solvent solution. Substituting may use more than 5 equivalents in relation to the imidazole nitrogens to be substituted.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/862,921 filed Jun. 7, 2004 and entitled “PolybenzimidazoleCompounds, Polymeric Media, And Methods Of Post-PolymerizationModifications,” the entire subject matter of which is incorporatedherein by reference.

GOVERNMENT RIGHTS

This invention was made with Government support under ContractDE-AC07-99ID13727 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

TECHNICAL FIELD

The invention pertains to polybenzimidazole compounds, polymeric mediaincluding polybenzimidazole compounds, and methods of makingpost-polymerization molecular modifications of polybenzimidazole.

BACKGROUND OF THE INVENTION

Polybenzimidazole (PBI) constitutes a well known class of heterocyclicpolymers and is described, merely by way of example and not limitation,in U.S. Pat. No. 4,814,400 issued to Sansone. One PBI known aspoly-2,2′(m-phenylene)-5,5′-bibenzimidazole has been used, as well asother PBI compounds, to form ionically conductive materials, fireresistant materials, and various types of separatory media, such asmembranes and ultrafilters. Poly-2,2′(m-phenylene)-5,5′-bibenzimidazoleis resistant to strong acids, bases, and high temperatures up to 500° C.but exhibits very poor solubility in common organic solvents. It issoluble under harsh conditions in highly polar, aprotic organicsolvents, such as dimethyl sulfoxide (DMSO), N,N-dimethylacetamide(DMAc), N,N-dimethylformamide (DMF), and N-methyl pyrrolidinone (NMP),which exhibit high boiling points and low vapor pressures. Accordingly,such solvents are not preferred for polymer processing.

As such, it would be advantageous to modify a PBI, such aspoly-2,2′(m-phenylene)-5,5′-bibenzimidazole, to exhibit bettersolubility in common organic solvents more preferable for polymerprocessing. Also, an appropriate method for modifying PBI would beadvantageous.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a polybenzimidazole (PBI)compound includes imidazole nitrogens at least 85% of which aresubstituted with a moiety containing a carbonyl group. The substitutedimidazole nitrogens are bonded to carbon of the carbonyl group. By wayof example, the carbonyl-containing moiety may include RCO—, where R isorganic and optionally contains an inorganic component. R may consist ofalkoxy or haloalkyl. Substantially all of the imidazole nitrogens may besubstituted with the RCO— moiety. The PBI compound may exhibit a firsttemperature marking an onset of weight loss corresponding to reversionof the substituted PBI, the first temperature being less than a secondtemperature marking an onset of decomposition of an otherwise identicalPBI compound without the substituted moiety.

As an alternative, the PBI compound includes imidazole nitrogens atleast a portion of which are substituted with a RCO— moiety, where R isorganic and optionally contains an inorganic component. The substitutedimidazole nitrogens are bonded to carbon of the RCO— moiety carbonylgroup and R is bonded to the carbon of the carbonyl group by other thana C—O bond.

According to another aspect of the invention, a polymeric mediumincludes the PBI compounds described above.

According to a further aspect of the invention, a PBI synthesis methodincludes providing PBI having imidazole nitrogens, reacting the PBI witha compound containing a carbonyl group, and substituting at least 85% ofthe imidazole nitrogens with a moiety from the compound. The substitutedimidazole nitrogens are bonded to carbon of the carbonyl group. By wayof example, the PBI may be provided in a less than 5 wt % solution ofthe PBI in a solvent, such as about 2.5 wt %. The method may furtherinclude ionizing the imidazole nitrogens before the reacting. Theionizing may involve deprotonating with an alkali metal hydride. Theionizing, reacting, and/or substituting may occur at from about 20 toabout 30° C. and/or at about atmospheric pressure. Reacting the PBI witha carbonyl-containing compound may use more than 5 equivalents of thecompound in relation to the imidazole nitrogens to be substituted, suchas about 10-15 equivalents. The compound may be RCOX, where R isorganic, optionally containing an inorganic component, and X is aleaving group. R may consist of alkoxy or haloalkyl. X may includehalogen, cyano, thiocyano, oxycyano, thioalkyl, alkoxy, fluoroalkoxy,sulfonylalkyl, oxyaromatic, thioaromatic, sulfonylaromatic, aromatic andalkyl carbodiimides, N-hydroxysuccinimide, oxyphosphorus containingcompounds, or oxysilane containing compounds. For example, RCOX mayinclude at least one of the following: (CH₃)₂CHCH₂OCOCl, CH₃CH₂OCOCl,and BrCH₂(CH₂)₃COCl.

As an alternative, a substituted PBI synthesis method includes providingPBI having imidazole nitrogens, reacting the PBI with a RCOX compound,where R is organic, optionally containing an inorganic component, and Xis a leaving group, and substituting at least a portion of the imidazolenitrogens with a RCO— moiety from the compound. The substitutedimidazole nitrogens are bonded to carbon of the RCO— moiety carbonylgroup and R is bonded to the carbon of the carbonyl group by other thana C—O bond.

According to a still further aspect of the invention, a polymeric mediumfabrication method includes forming a polymeric medium that includes thesubstituted PBI compounds described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 shows the chemical structure ofpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole.

FIG. 2 shows the chemical structure ofpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole substituted with anorganic-inorganic hybrid moiety.

FIG. 3 shows the ¹H NMR analytical results forpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole.

FIG. 4 shows the ¹H NMR analytical results for (CH₃)₂CHCH₂OCO—substituted poly-2,2′(m-phenylene)-5,5′-bibenzimidazole.

FIG. 5 shows the ¹H NMR analytical results for CH₃CH₂OCO— substitutedpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole.

FIG. 6 shows the ¹H NMR analytical results for BrCH₂(CH₂)₃CO—substituted poly-2,2′(m-phenylene)-5,5′-bibenzimidazole.

FIG. 7 shows the ¹³C{¹H} NMR analytical results for CH₃CH₂OCO—substituted poly-2,2′(m-phenylene)-5,5′-bibenzimidazole.

FIG. 8 shows a reaction sequence that forms polybenzimidazole (PBI)substituted with a carbonyl-containing moiety.

FIG. 9 shows a reaction sequence and mechanism that reverts substitutedPBI back to the parent PBI.

FIG. 10 shows the schematic representation of the time-lag pure gaspermeability measurement method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

PBI may be synthetically modified to produce a polymer soluble in awider range of organic solvents, including those preferred for polymerprocessing. The synthetic modification can be accomplished by exploitingthe reactive imidazole nitrogens of PBI with polymer substitution(grafting) or by altering monomers and subsequently forming the desiredpolymer. Since a variety of PBI compounds can be acquired commercially,substitution of the polymer is preferred. Altering monomers andsubsequently forming the desired polymer can be difficult and theresulting polymer molecular morphology can be considerably differentfrom the intended parent PBI. However, previous attempts to enhance PBIsolubility in common solvents by substitution of PBI met with littlesuccess.

Some of the attempts at modifying PBI relying upon the reactiveimidazole nitrogens include substitution as well as cross-linking. (U.S.Pat. Nos. 4,020,142 and 4,154,919). Blending PBI with aromaticpolyamides, aromatic polyamide-hydrazides, and aromatic polyamides withheterocyclic linkages is also known. (U.S. Pat. No. 5,290,884). However,in all of such efforts, solubility of the PBI remains a problem and thetypical product forms a paste or gel (referred to in industry as a“dope”) in strong acidic conditions. Substitution of PBI includesmodification with an omega halo alkanol or a 1,2-alkylene oxide to makehydroxyl substituted PBI. (U.S. Pat. No. 3,578,644). Other pathways areknown to produce hydroxyl substituted PBI. (U.S. Pat. No. 4,599,388).Substituted PBI has also been formed by reacting substituted tetraaminopyridines or their organic salts with a suitable acid halide or acidanhydride and cross-linking the result to yield PBI. (U.S. Pat. No.3,943,125). N-aryl substituted PBI is also known. (U.S. Pat. No.3,518,234). However, in each circumstance no increase of polymersolubility in common solvents was described.

In a series of patents, Sansone, et al. describes a variety of pathwaysfor substitution of PBI. (U.S. Pat. No. 4,814,399, No. 4,997,892, No.4,814,400, No. 4,868,249, No. 4,898,917, and No. 4,933,397). Even so, noindication is given that any of the resulting substituted PBI exhibiteda solubility increase in common solvents compared to the original PBI.It is apparent from the deficiencies of the conventional productsresulting from known PBI modification methods that it would be anadvantage to provide a modified PBI exhibiting enhanced solventsolubility.

In addition, the methods described in the Sansone patents listed aboveused process conditions only obtainable with specialized equipment. Forexample, reaction temperatures greater than 50° C., reaction pressuresgreater than 2 atmospheres, and a PBI concentration in the startingpolymer solution of greater than 5 weight percent (wt %). Suchconditions were obtained with heated and pressurized reaction chambersand a relatively viscous polymer solution that all complicatedproduction of a substituted PBI. The maximum degree of substitution was83.3% and higher relative concentrations of reactants did not increasethe degree of PBI substitution. U.S. Pat. No. 4,898,917 also stated thatwhen the polymer solution contains less than about 5% concentration ofPBI, the substitutions obtained are less than optimum.

As may be appreciated, a variety of areas exist wherein conventional PBIcompounds and methods of making such compounds may be improved.According to one aspect of the invention, PBI compound includesimidazole nitrogens at least a portion of which are substituted with amoiety containing a carbonyl group. The substituted imidazole nitrogensare bonded to carbon of the carbonyl group. As one example, the compoundmay be a substituted poly-2,2′(m-phenylene)-5,5′-bibenzimidazole as wellas other substituted PBI compounds. At least 85% of the imidazolenitrogens may be substituted with the carbonyl-containing moiety, thoughpreferably, substantially all of the imidazole nitrogens are sosubstituted.

As will be understood by those of ordinary skill, conventional analysismay be used to determine the approximate degree of substitution. Sincethe molecular weight of PBI can be rather high, some small number ofimidazole nitrogens might be cross-linked or otherwise not substitutedby the organic-inorganic hybrid moiety. Yet, within the sensitivity ofconventional analytic techniques, the PBI may give an indication thatall of the imidazole nitrogens are so substituted. Understandably then,when “substantially all” of the imidazole nitrogens are so substituted asmall number of nitrogens may be cross-linked or otherwise notsubstituted, but such a small number would be insignificant in light ofthe purposes described herein for improvement upon conventional PBIcompounds.

Also, although a preference exists for substitution of the imidazolenitrogens with a single compound, such as the carbonyl-containingmoiety, it is conceivable that multiple different compounds may be used.Carbonyl-containing compounds constitute one class of moietiespossessing significant advantages previously unrecognized. Somecarbonyl-containing moieties demonstrated to impart beneficialproperties include RCO— where R is at least one of isobutoxy, ethoxy,and 4-bromobutyl (respectively, (CH₃)₂CHCH₂OCO—, CH₃CH₂OCO—, andBrCH₂(CH₂)₃CO—). Even so, other carbonyl-containing moieties may beadvantageous as well. In general, the carbonyl-containing moiety may beRCO—, wherein R is alkoxy or haloalkyl. Bromoalkyl is a suitable moiety.The alkoxy or haloalkyl may bond to the imidazole nitrogens to form,respectively, a carbamate or an amide.

The R portion of the moiety might be evaluated and selected to providesimilar, different, or additional advantages in comparison to thespecific compounds listed above. Accordingly, more generally, R may beorganic and optionally contain an inorganic component. As an example Rmay include alkyl, aryl, alkenyl, or alkynyl and the inorganic componentmay include oxygen, nitrogen, scandium, yttrium, titanium, zirconium,hafnium, vanadium, niobium, molybdenum, tungsten, iron, ruthenium,cobalt, rhodium, nickel, palladium, platinum, boron, aluminum, gallium,indium, silicon, germanium, tin, phosphorus, arsenic, antimony, sulfur,selenium, tellurium, or oxides thereof. R may be bonded to the carbon ofthe carbonyl group by other than a C—O bond. One example includes a C—Cbond, such as when R consists of haloalkyl.

Many unsubstituted PBI compounds used in commercial applications areknown for their stability and advantageous thermal properties, such as ahigh glass transition temperature (T_(g)). The T_(g) ofpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole is 435° C. Substitution ofPBI can potentially modify thermal properties of the parent compound anddiminish the advantageous thermal stability. A substituted PBI inkeeping with the aspects of the invention may exhibit similar, or evenimproved, thermal stability in comparison to the unsubstituted PBI.

Even though it may be desirable in many situations for the thermalproperties of the PBI to remain largely unchanged after substitution, itmay be desirable for the substitution to intentionally alter thermalproperties. For example, as shown in FIG. 9, a substituted PBI mayrevert to the parent PBI upon heating. That is, a substituted PBI mayexhibit a first temperature marking an onset of weight losscorresponding to reversion of the substituted PBI, the first temperaturebeing less than a second temperature marking an onset of decompositionof an otherwise identical PBI compound without the substituted moiety.The first temperature may be at least 50° C. less than the secondtemperature.

Accordingly, substitution may yield a lower decomposition temperature inan initial heating cycle. The heating may occur at a temperature highenough to remove all of the substituted functional groups during theinitial heating cycle as the substituted PBI reverts to the parent PBI.Subsequent heating cycles at a similar temperature may not affect theparent PBI. Thus, PBI may be substituted with functional groups thatrender it easier to manipulate in a particular application, such as filmforming, and subsequently heat treated to revert to the original PBI.This thermoset type of behavior can enable improvement upon the inherentprocessing difficulties associated with PBI while still allowing thefinal product to contain the unsubstituted PBI.

Unsubstituted or substituted conventional PBI is known to exhibit poorsolubilities in common solvents. Such property is demonstrated at leastin U.S. Pat. No. 4,814,400 issued to Sansone and discussed above. It isapparent from Sansone that thepoly-2,2′(m-phenylene)-5,5′-bibenzimidazole was difficult to use,prompting processing with a highly polar, aprotic organic solvent atelevated temperatures and pressures in a sealed vessel to completelydissolve PBI into solution. Even so, the polymer solution was quiteviscous and filtering to remove undissolved PBI was recommended. Thoseof ordinary skill encounter similar difficulties when attempting tofabricate products that include PBI.

Accordingly, it is a significant advantage that the PBI compoundaccording to the aspects of the invention exhibits solubility in anorganic solvent greater than the solubility of the unsubstituted PBI.The PBI compound may exhibit a solubility in tetrahydrofuran (THF),chloroform, or dichloromethane of at least about 0.01 grams permilliliter of solvent (g/mL), or preferably at least about 0.2 g/mL.Such solubility may be exhibited within about 30 minutes or less at roomtemperature. Longer periods for full dissolution to occur and/or highertemperatures are less preferred.

In another aspect of the invention, a polymeric medium includes a PBIcompound having imidazole nitrogens at least a portion of which aresubstituted with a moiety containing a carbonyl group. The substitutedimidazole nitrogens are bonded to carbon of the carbonyl group. The PBIcompound may have a similar composition and exhibit similar propertiesto those described above. As may be appreciated, tailoring thermalproperties of the parent PBI and enhancing solvent solubility may beparticularly advantageous in forming a polymeric medium. Possibleapplications for the polymeric medium that includes the substituted PBIinclude, without limitation, ¹³C NMR analysis, carbon-14 radioactivelabeling, silica imprints, synthetic transformations, ink-jet printing,and lithography. The polymeric medium may be separatory, electronicallyconductive, and/or ionically conductive.

The term “separatory medium” encompasses a variety of materials,including but not limited to membranes (semi-permeable, permeable, andnon-permeable), barriers, ion exchange media, filters, gaschromatography coatings (such as stationary phase coatings in affinitychromatography), etc. The separatory medium including such a substitutedPBI compound may exhibit a H₂, Ar, N₂, O₂, CH₃, and/or CO₂ gaspermeability greater than the gas permeability of a comparable polymericmedium instead comprising the unsubstituted PBI compound. Thesubstituted PBI compound may be used and/or modified in the same mannerthat poly-2,2′(m-phenylene)-5,5′-bibenzimidazole or other known PBIcompounds have been or may be used and/or modified by those of ordinaryskill to function as separatory media. For example, U.S. Pat. Nos.4,693,824 and 4,693,825, both issued Sep. 15, 1997, as well as otherreferences, describe forming separatory media.

Electronically conductive media may be membranes and/or materials thatare useful in fabrication of nanowires, organic conductors, organicelectronic devices, and the like. The substituted PBI compound may beused and/or modified in the same manner thatpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole or other known PBI compoundshave been or may be used and/or modified by those of ordinary skill tofunction as electronically conductive media. For example, U.S. Pat. No.4,759,986, issued Jul. 26, 1988, and U.S. Pat. No. 5,017,420, issued May21, 1991, as well as other references, describe forming electronicallyconductive media.

Ionically conductive media may be membranes and/or materials that areuseful in fabrication of semi-fuel cells, fuel cells, and the like, suchas for proton exchange membranes and/or polymer electrolyte membranes.The substituted PBI compound is well-suited for the potentiallycorrosive environment of semi-fuel cells and fuel cells. The substitutedPBI compound may be used and/or modified in the same manner thatpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole or other known PBI compoundshave been or may be used and/or modified by those of ordinary skill tofunction as ionically conductive media. For example, U.S. Pat. No.5,599,639, issued Feb. 4, 1997, and U.S. Pat. No. 6,124,060, issued Sep.26, 2000, as well as other references, describe forming ionicallyconductive media.

In addition to improved PBI compounds, the aspects of the invention alsoinclude improvements in methods for making substituted PBI compounds andproducts comprising such compounds.

According to a further aspect of the invention, a substituted PBIsynthesis method includes providing PBI having imidazole nitrogens,reacting the PBI with a compound containing a carbonyl group, andsubstituting at least a portion of the imidazole nitrogens with a moietyfrom the compound. The substituted imidazole nitrogens are bonded tocarbon of the carbonyl group. By way of example, the PBI may be providedin a less than 5 wt % solution of the PBI in a solvent. Suitablesolvents include DMSO, DMAc, DMF, NMP, and others known to those ofordinary skill. A 2.5 wt % solution of the PBI in a solvent has proveneffective. The method may further include ionizing the imidazolenitrogens, for example, by deprotonating with an alkali hydride. Sodiumhydride (NaH) and other alkali hydrides known to those of ordinary skillare suitable.

The carbonyl-containing compound may be RCOX, where R is alkoxy orhaloalkyl and X is halogen, preferably Cl. More generally, R may beorganic, optionally containing an inorganic component, and X may be aleaving group. R may include alkyl, aryl, alkenyl, or alkynyl and theinorganic component may include oxygen, nitrogen, scandium, yttrium,titanium, zirconium, hafnium, vanadium, niobium, molybdenum, tungsten,iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, boron,aluminum, gallium, indium, silicon, germanium, tin, phosphorus, arsenic,antimony, sulfur, selenium, tellurium, or oxides thereof. X may includehalogen, cyano, thiocyano, oxycyano, thioalkyl, alkoxy, fluoroalkoxy,sulfonylalkyl, oxyaromatic, thioaromatic, sulfonylaromatic, aromatic andalkyl carbodiimides, N-hydroxysuccinimide, oxyphosphorus containingcompounds, or oxysilane containing compounds.

One advantage of the method includes performing process steps at roomtemperature and/or pressure. The ionizing may occur at from about 20 toabout 30° C. The reacting and substituting can occur at from about 20 toabout 30° C. As another advantage, the ionizing, reacting, and/orsubstituting may occur at about atmospheric pressure. The reacting mayuse more than 5 equivalents of the carbonyl-containing compound inrelation to the imidazole nitrogens to be substituted. Preferably, thereacting uses at least 10 equivalents, for example about 10-15equivalents, of the carbonyl-containing compound.

The use of such a high number of carbonyl-containing compoundequivalents contradicts the teachings of conventional processes asindicated at least in U.S. Pat. No. 4,814,400. Such patent indicatesthat more than 5 equivalents fails to achieve significantly highersubstitutions than obtained between 1 and 5 equivalents and the highestdegree of substitution obtained in such patent was 83.3%. In accordancewith the aspects of the present invention, substantially all of theimidazole nitrogens may be substituted with the carbonyl-containingmoiety. Observations indicated that the higher number of equivalents hadthe surprising effect of rendering the substituted PBI solvent solublewhile a substituted PBI produced using 5 or fewer equivalents onlyexhibited slight solvent solubility.

According to another aspect of the invention, a separatory mediafabrication method includes providing PBI having imidazole nitrogens,reacting the PBI with a compound containing a carbonyl group,substituting at least a portion of the imidazole nitrogens with a moietyfrom the compound, and forming a separatory media that contains thesubstituted PBI. The substituted imidazole nitrogens are bonded tocarbon of the carbonyl group. Providing, reacting, and substituting thePBI may be performed in accordance with the methods described above forsubstituted PBI synthesis. As an example, one advantage of separatorymedia formed by such method is that it may exhibit a H₂, Ar, N₂, O₂,CH₃, and/or CO₂ gas permeability greater than the gas permeability of acomparable separatory media that instead comprises the PBI.

Suitable substituted PBI syntheses are described in Examples 1-3 belowand summarized in FIG. 8.

EXAMPLE 1

A parent PBI solution was made by pulverizing 5 g ofpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole (available commercially asCelazole™) to a fine powder and placing it into a 250 mL round bottomflask. The flask was equipped with a water-jacketed condenser, gas inletadaptor, and magnetic stir bar. The system was placed under vacuum for 5to 8 hours and the system was then purged with nitrogen. Anhydrous DMAc(200 mL) was transferred to the flask and the solution was heated toboiling with stirring for about 24 hours. The solution was allowed tocool to room temperature.

The cooled parent PBI solution (32 mL; 0.0013 mol of the polymerrepeating unit, each having two reactive N—H sites) was filtered througha 0.45 μm PTFE filter by syringe and transferred into a 100 mL roundbottom flask equipped with a gas inlet adapter and magnetic stir bar andcharged with nitrogen. NaH (80% in oil dispersion) (180 mg; 0.0063 mol)was directly added to the PBI solution and stirred for about 6 hours atroom temperature. During this time, a deep red/violet color andincreased viscosity of the solution was observed. After most of the NaHwas consumed, a substitution compound containing a carbonyl group((CH₃)₂CHCH₂OCOCl; 5 mL; 0.039 mol; 15 equivalents per N—H site) wasadded via syringe to the flask. The reaction mixture color changed to alight yellowish brown after the carbonyl compound addition. Thissolution was stirred for 48 hours at room temperature. The solutioncolor returned to a yellowish-brown (similar to the parent PBI) duringthis time. Compound 1 shown in FIG. 2 was formed.

Upon completion, the reaction solution was transferred directly into a2000 mL beaker filled with de-ionized, nanopure water (1200 mL). Thepolymer immediately precipitated in water as a yellow-brown solid. Thewater-polymer solution was mixed well and filtered through fluted filterpaper. The collected polymer was transferred to a crystallizing dish toair-dry overnight. The next day, the dry polymer was dissolved in THF(50-150 mL). Sonication was used to disperse and affect dissolution ofthe polymer in the solution. This THF solution was filtered throughfluted filter paper. Any collected solids were set aside, and theyellow-brown, polymer-containing THF solution was condensed to a minimalamount.

This solution was added drop wise to a 2000 mL beaker filled withhexanes (1000-1200 mL). The polymer precipitated as light-yellowfeathery solid or light-yellow flakes. The hexanes solution was mixedwell and the solids were allowed to settle. The hexanes polymer solutionwas decanted through a paper filter or filtered through a vacuumaspirator equipped with a 5.0 μm nylon filter. The polymer was collectedfrom the filter paper and dried under vacuum to give a near quantitativeyield. Yield of the substituted PBI was 95 wt % of the parent PBI asshown in Table 1.

NMR analysis was used to identify the modified PBI products in CDCl₃ asshown in FIG. 4 and may be compared to NMR analysis of the parent PBI ind₆-DMSO shown in FIG. 3. NMR spectra were recorded on a Bruker DMX 300WBspectrometer operating at 7.04 T: 300 MHz (¹H) and 75 MHz (¹³C{¹H}, ifperformed).

A description of the parent PBI NMR spectra is as follows withdesignated H atoms such as H_(a), H_(b), etc. shown in FIG. 2: ¹H NMR δ(d₆-DMSO)=(s, H_(a), 2H) 9.17, (broad multiplet, H_(b), 2H) 8.30-8.38,(s, H_(c), 2H) 8.06, (broad multiplet, H_(d), 1H) 7.75-7.90, (broadmultiplet, H_(e), 1H) 7.60-7.75; ¹³C{¹H} NMR δ (d₆-DMSO)=(s, aromatic)153.1, (s, aromatic) 143.8, (s, aromatic) 142.5, (s, aromatic) 137.0,(s, aromatic) 135.8, (s, aromatic) 131.9, (s, aromatic) 131.0, (s,aromatic) 130.3, (s, aromatic) 129.6, (s, aromatic) 122.9, (s, aromatic)120.1, (s, aromatic) 118.5, (s, aromatic) 111.1, (s, aromatic) 109.7.

A description of the substituted PBI (compound 1) NMR spectra is asfollows: ¹H NMR δ (CDCl₃)=(broad multiplet, aromatic) 8.30-8.40, (broadmultiplet, aromatic) 8.10-8.25, (broad multiplet, aromatic) 7.80-7.90,(broad multiplet, aromatic) 7.70-7.80, (broad multiplet, aromatic)7.60-7.70, (broad multiplet, CH₂, 2H) 4.10-4.25, (broad multiplet, CH,1H) 0.95-1.15, (broad multiplet, (CH₃)₂, 6H) 0.60-0.95.

EXAMPLE 2

Example 1 was repeated using CH₃CH₂OCOCl (5 mL; 0.052 mol; 20equivalents per N—H site) as the carbonyl-containing compound, formingcompound 2 shown in FIG. 2. Yield of the substituted PBI was 95 wt % ofthe parent PBI as shown in Table 1. NMR analysis was used to identifythe products in CDCl₃ as shown in FIGS. 5 and 7. A description of thesubstituted PBI (compound 2) NMR spectra is as follows: ¹H NMR δ(CDCl₃)=(broad multiplet, aromatic) 8.35-8.50, (broad multiplet,aromatic) 8.25-8.35, (broad multiplet, aromatic) 8.00-8.25, (broadmultiplet, aromatic) 7.75-7.95, (broad multiplet, aromatic) 7.60-7.75,(broad multiplet, CH₂, 1H) 4.30-4.50, (broad multiplet, CH₃, 3H)1.15-1.40; ¹³C{¹H} NMR δ (CDCl₃)=(aromatic range, multiple peaks)113.0-154.3, (s, CH₂) 64.9, (s, CH₃) 15.0.

EXAMPLE 3

Example 1 was repeated using (BrCH₂(CH₂)₃COCl (5 mL; 0.037 mol; 14 moleequivalents per N—H site) as the carbonyl-containing compound, formingcompound 3 shown in FIG. 2. Yield of the substituted PBI was 20 wt % ofthe parent PBI as shown in Table 1. NMR analysis was used to identifythe products in CDCl₃ as shown in FIG. 6. A description of thesubstituted PBI (compound 3) NMR spectra is as follows: ¹H NMR δ(CDCl₃)=(broad multiplet, aromatic) 8.75-9.00, (broad multiplet,aromatic) 8.15-8.25, (broad multiplet, aromatic) 8.00-8.15, (broadmultiplet, aromatic) 7.80-8.00, (broad multiplet, aromatic) 7.50-7.70,(broad multiplet, CH₂, 2H) 3.25-3.75, (broad multiplet, CH₂, 2H)2.20-2.60, (broad multiplet, (CH₂)₂, 6H) 1.50-2.10.

EXAMPLE 4 Molecular Weight Analysis

Dilute solution techniques are used to characterize the macromolecularstructure of the polymers. 0.2 μm-filtered THF is used as the solventand the analyses are performed at 25° C. Solution refractive indexincrement, dn/dc values are obtained using a Rainin Dynamax RI-1refractive index detector. High performance size exclusionchromatography (HPLC) is performed using a Waters Model 2690solvent/sample delivery system with a column bank of two Styragel HR 5E(4.6 mm id.×300 mm) solvent efficient columns. The columns are keptisothermal and operated with a solvent flow rate of 0.3 mL/min. Thepolymer solutions are filtered through a 0.45 μm filter prior toinjection onto the columns. Detection is achieved using a WyattTechnologies DAWN-EOS laser light scattering detector with the K5 flowcell that measures scattered light intensities at angles ranging from14.7° to 158.2°. The Dynamax RI-1 refractive index detector is placed inseries with the light scattering detector as a concentration detector.Weight average molecular weight (M_(w)) and number average molecularweight (M_(n)) are determined and the polydispersity index (PDI)(M_(w)/M_(n)) calculated as an indication of the distribution ofindividual molecular weights in the batch of polymers. The molecularweight of the parent PBI is approximately 20,000 g/mol. Similarsubstituted PBI compounds previously synthesized exhibited molecularweights above 250,000 g/mol (see related U.S. patent application Ser.No. 10/862,921 filed Jun. 7, 2004 entitled “Polybenzimidazole Compounds,Polymeric Media, And Methods Of Post-Polymerization Modifications”).TABLE 1 Yield. Yield Polymer (percent) Parent PBI NA(CH₃)₂CHCH₂OCO—(PBI) (1) 95 CH₃CH₂OCO—(PBI) (2) 95 BrCH₂(CH₂)₃CO—(PBI)(3) 20

EXAMPLE 5 Thermal Analysis

Thermal analyses were obtained using TA Instruments Model 2910differential scanning calorimeter (DSC) and a Model 2950thermogravimetric analyzer (TGA). As indications of thermal stability,an attempt was made to determine T_(g) and melt transition temperature(T_(m)). In a first heating cycle, a sample was heated to about 300° C.Compounds 1 and 2 showed sharp exothermic transitions in the DSC atrespective temperatures of 270 and 221° C. (at a heating ramp rate of10° C./min). In a second heating cycle, after cooling to roomtemperature and without removing the sample from the DSC chamber, thesample was heated to about 300° C. and the first cycle exotherm was notobserved. However, slowing the heating ramp rate to 1° C./min droppedthe compound 2 exotherm to 188° C. This drop often occurs with manycompounds exhibiting an exotherm. It provides a way to slowly evolve offthe gases.

As another indication of thermal stability, a determination was made ofthe temperature at which onset of decomposition occurred. Data aresummarized in Table 2. The thermal gravimetric analysis of compounds 1and 2 provides thermal properties expected for a carbamate. Their 22-23%weight loss is consistent with CO₂ and alkene evolution. The initialweight loss temperatures for compounds 1 and 2 are within 50° C. of eachother. A slow heating cycle apparently removed all of the functionalgroups. The next weight loss for compounds 1 and 2 occurred at about470-480° C., close to the parent PBI polymer initial weight losstemperature.

The exothermic behavior of compounds 1 and 2 was studied further bycasting both as films. One set of films was subjected to a slow heatingcycle (1° C./min) to 200° C. in a furnace exposed to the ambientatmosphere. Another set was used as a control. Both compounds 1 and 2released the CO₂ and alkene without destroying the bulk film during theheating cycle. Both sets of films were analyzed by ESEM (EnvironmentalScanning Electron Microscopy) for consistency and the ESEM showed thatthe heat-treated film remained intact. Further examination of the filmsshowed large voids prior to the heating cycle. However, the voidsdisappeared and the films showed significant compaction upon heating.This is consistent with CO₂ and alkene evolution, therefore it can bepostulated that the carbamate PBI polymers reverted to the parentmaterial. TABLE 2 Differential Scanning Calorimetry and ThermalGravimetric Analysis Data. Initial Weight Loss and Polymer T_(g) and/orT_(m) Temperature in N₂ Parent PBI T_(g) = 435° C.^(a) 512° C.(CH₃)₂CHCH₂OCO—(PBI) (1) T_(exo) = 270° C.^(b) 23% wt. loss at (firstheating cycle) 252° C.^(b) 15% wt. loss at 480° C.^(b)(CH₃)₂CHCH₂OCO—(PBI) (1) d^(b) e (second heating cycle) CH₃CH₂OCO—(PBI)(2) T_(exo) = 221° C.^(b) 22% wt. loss at (first heating cycle) T_(exo)= 188° C.^(c) 216° C.^(b) 12% wt. loss at 470° C.^(b) CH₃CH₂OCO—(PBI)(2) d^(b) e (second heating cycle) BrCH₂(CH₂)₃CO—(PBI) (3) e e^(a)From manufacturer.^(b)Heating ramp rate = 10° C./min.^(c)Heating ramp rate = 1° C./min.^(d)No detectable thermal exotherms/endotherms up to 500° C.^(e)To be determined.

EXAMPLE 6 Gas Permeability

Gas permeability testing was performed using the time-lag method.Membranes were exposed to six different gases: He, H₂, N₂, O₂, CH₄ andCO₂. The interactions of the test gases and the polymer membranes wereinterpreted using the solution-diffusion model. FIG. 10 provides aschematic representation of the time-lag pure gas permeabilitymeasurement apparatus.

Turning to FIG. 10, a measurement apparatus 10 includes a membrane 42formed on a porous support 44 and placed in a test cell 38 againstO-ring 40 so as to seal a feed side of membrane 42 from the permeateside. Both sides of the membrane 42 (including the tubing, a feedreservoir 12, and a permeate reservoir 14) were evacuated to an equalvacuum using vacuum lines 18 and 20 with vacuum valves 28 and 30 open.Vacuum valves 28 and 30 along with an isolation valve 36 were closed,isolating test cell 38. Apparatus 10 was checked for leaks and the driftin pressure readings, if any, was characterized. A pressure baseline atzero time on the permeate side of membrane 42 was noted using adifferential pressure transducer 24 providing a data signal through adata line 34. A feed valve 26 was opened and feed reservoir 12 filledthrough a feed line 16 to a desired initial feed pressure of the testgas as indicated by a pressure transducer 22 providing a data signalthrough a data line 32. Next, isolation valve 36 was opened, exposingthe feed side of membrane 42 to the test gas. The pressure build-up onthe permeate side of the membrane as a function of time was recorded.Previous to the testing, the volume of the permeate reservoir 14, theassociated tubing, etc. on the permeate side of membrane 42 was wellcharacterized to allow accurate calculations from the test data. The twovalues determined directly from the pure gas test system includedtime-lag and permeability.

Permeability is the rate at which the gas permeates through the membraneafter the gas comes to equilibrium in the polymer. From initialintroduction of the feed gas to the membrane, permeate pressureincreases in a non-linear manner until the gas comes to equilibrium inthe polymer. After reaching equilibrium, permeate pressure increaseslinearly with respect to time. Time-lag is the time that it takes thegas to permeate from the feed side of the membrane to the permeate sideand is used to calculate the diffusivity. The basic relationship of thegas transport properties permeability (P), solubility (S), anddiffusivity (D) in polymeric membranes is expressed in the followingterms.P=DS   Equation 1Permeabilities for these experiments were calculated using the followingequations where test system volume is V (cm³), test system feed gasinitial pressure is p₁ (cm Hg), test system temperature is T (° C.),membrane thickness is l (cm), and membrane area exposed to the feed gasis A (cm²). Slope was determined from a least squares fitted line of thetime (sec) versus permeate gas pressure (cm Hg) steady state data set(data during equilibrium flux) obtained using the above method.$\begin{matrix}{P = {{slope}\quad\frac{V}{76}\frac{273}{\left( {273 + T} \right)}\frac{1}{A}\frac{l}{p_{1}}}} & {{Equation}\quad 2}\end{matrix}$Time-lag is the intercept of the permeate gas initial pressure baselineand the least square fitted line for the data set. Given the slope andpressure axis intercept from the least square fitted line according to ay=ax+b formula wherein pressure=slope×time+intercept, time-lag may becalculated using $\begin{matrix}{t = {{timelag} = \frac{{baseline} - {intercept}}{slope}}} & {{Equation}\quad 3}\end{matrix}$and then the determined value for the time-lag used to calculate thediffusivity D.D=l ²/6t   Equation 4

Gas solubility is algebraically calculated from the measured quantitiesof permeability and diffusivity using Equation 1. Data are summarized inTable 3. TABLE 3 Gas Testing Permeability.^(a) Polymer H₂ Ar N₂ O₂ CH₄CO₂ Parent PBI @ 30° C. 3.9 0.073 0.049 0.086 0.04 0.07 Parent PBI @ 55°C. 5.7 0.07 0.09 0.31 0.11 0.25 (CH₃)₂CHCH2OCO-(PBI) (1) 27.7 1.0 0.51.9 1.8 18.7 (before heat treatment) (CH₃)₂CHCH2OCO-(PBI) (1) ^(c) ^(c)^(c) ^(c) ^(c) ^(c) (after heat treatment) CH₃CH₂OCO-(PBI) (2) 89 ^(b)^(b) ^(b) 35 47 (before heat treatment) CH₃CH₂OCO-(PBI) (2) ^(c) ^(c)^(c) ^(c) ^(c) ^(c) (after heat treatment) BrCH₂(CH₂)_(CO-(PBI) (3))^(c) ^(c) ^(c) ^(c) ^(c) ^(c)${\quad^{a}{Permeabilities}\quad{in}\quad{Barrers}},\quad{10^{- 10} \cdot {\left( \frac{{cm}_{{gas} - {STP}}^{3} \times {cm}}{{cm}^{3} \times \sec \times {cm}\quad{Hg}} \right).}}$^(b)Not analyzed. ^(c)To be determined.

EXAMPLE 7 Solvent Solubility

Quantitative solvent solubility testing was performed in THF,chloroform, and dichloromethane. Qualitative observations of solubilitywere made for DMAc and NMP. Unless otherwise indicated, the solventsolubility data was obtained 30 minutes after addition to the solvent atroom temperature or an otherwise indicated temperature. TABLE 4 SolventSolubility. Solubility - grams/mL of Solvent Polymer THF CHCl₃ CH₂Cl₂DMAc NMP Parent PBI^(a) Not Not Not Partially Partially Soluble SolubleSoluble soluble soluble (CH₃)₂CHCH₂OCO—(PBI) (1)  0.3-0.25  0.3-0.25^(b) 0.3-0.25^(b) Soluble Soluble CH₃CH₂OCO—(PBI) (2) 0.25-0.2 0.25-0.2^(b)0.25-0.2^(b) Soluble Soluble^(a)Soluble in DMSO; partially soluble in DMF; 0.05-0.06 g/mL in formicacid. (Vogel, et al, J. Polym. Sci., vol. 50, pg. 511, 1961).^(b)Elevated temperature (˜50° C.) and constant stirring.^(c)Not tested.

A number of observations may be made from the above Examples. The yieldsfor both the isobutyl chloroformate and ethyl chloroformate wereapproximately 95%, however, the reactions that used 5-bromovalerylchlorideresulted in lower yields, 20%. In addition, some of the bromidewas eliminated from the alkyl chain to give a terminal alkene. This wasprobably due to the excess NaH in solution.

From the NMR analysis, the integration ratios of the ¹H NMR spectrashowed that roughly 100% of the PBI is substituted by thecarbonyl-containing compounds. The unsubstituted imidazole (N—H) was notapparent in the ¹H NMR spectrum at 9.2 ppm, and this was seen with allof the substituted polymers (FIGS. 2-6). The methylene (—CH₂OCO) for thecarbamate modified PBI polymers (compounds 1 and 2) were easilydetermined from both ¹H NMR (˜4.20-4.40 ppm) and ¹³C{¹H} NMR (˜65.0 ppm)spectra. The rest of the alkyl chain(s) for compound 1 (—CH₃ at 1.30ppm) and compound 2 (—CH— at 1.00 ppm and —CH₃ at 0.88 ppm) were alsoseen in the ¹H NMR. However, the methylene group next to the carbonyl(—CH₂CO) on compound 3 had a shift in the ¹H NMR at about 2.50 ppm. Therest of the alkyl chain on compound 3 was also identified through ¹HNMR. The functional group on compound 3 (—CH₂Br) can be clearly assignedfor the ¹H NMR spectra. In the aromatic region, four aromatic peaks werevery similar in the ¹H NMR spectra among compound 1-3 and parent PBIspectrum. All of the NMR data showed that compounds 1-3 are PBI modifiedmaterials.

The molecular weights expected for compounds 1-3, as discussed inExample 4, are likely an order of magnitude higher than themanufacturer's value for the parent PBI. This suggests that the parentPBI may have a higher molecular weight than indicated by themanufacturer or the PBI may cross-link, or exhibit continued livingpolymerization due to residual stable carbocations from the initialpolymer synthesis, during the post-polymerization syntheticmodification. A large polydispersity index (M_(w)/M_(n)) is alsoexpected for the substituted PBI. This suggests that the parent PBIstarting material does not have a narrow molecular weight range and thatthe manufacturer's value may exclude some of the larger molecularweights.

The gas testing of compounds 1-3 presents throughput values that areorders of magnitude better than the parent PBI (Table 3). However, notall of the gases are affected to the same extent. The H₂ and CO₂ valuesare the largest for compounds 1 and 2 while the other gas values arelower.

As may be appreciated from the description herein, the compounds,materials, and methods according to the aspects of the invention providea number of advantages in comparison to known compounds, materials, andmethods.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A polybenzimidazole (PBI) compound comprising imidazole nitrogens atleast 85% of which are substituted with a moiety containing a carbonylgroup, the substituted imidazole nitrogens being bonded to carbon of thecarbonyl group.
 2. The compound of claim 1 wherein substantially all ofthe imidazole nitrogens are substituted with the carbonyl-containingmoiety.
 3. The compound of claim 1 wherein the carbonyl-containingmoiety comprises RCO—, where R is organic and optionally contains aninorganic component.
 4. The compound of claim 3 wherein R consists ofalkoxy or haloalkyl.
 5. The compound of claim 1 wherein thecarbonyl-containing moiety comprises at least one of (CH₃)₂CHCH₂OCO—,CH₃CH₂OCO—, and BrCH₂(CH₂)₃CO—.
 6. The compound of claim 1 exhibiting afirst temperature marking an onset of weight loss corresponding toreversion of the substituted PBI, the first temperature being less thana second temperature marking an onset of decomposition of an otherwiseidentical PBI compound without the substituted moiety.
 7. The compoundof claim 6 wherein the first temperature is at least 50° C. less thanthe second temperature.
 8. A PBI compound comprising imidazole nitrogensat least a portion of which are substituted with a RCO— moiety, where Ris organic and optionally contains an inorganic component, thesubstituted imidazole nitrogens being bonded to the carbon of the RCO—moiety carbonyl group and R being bonded to the carbon of the carbonylgroup by other than a C—O bond.
 9. The compound of claim 8 wherein Rcomprises alkyl, aryl, alkenyl, or alkynyl and the inorganic componentcomprises oxygen, nitrogen, scandium, yttrium, titanium, zirconium,hafnium, vanadium, niobium, molybdenum, tungsten, iron, ruthenium,cobalt, rhodium, nickel, palladium, platinum, boron, aluminum, gallium,indium, silicon, germanium, tin, phosphorus, arsenic, antimony, sulfur,selenium, tellurium, or oxides thereof.
 10. The compound of claim 8wherein R is bonded to the carbon of the carbonyl group by a C—C bond.11. The compound of claim 10 wherein R consists of haloalkyl.
 12. Thecompound of claim 8 comprising substitutedpoly-2,2′(m-phenylene)-5,5′-bibenzimidazole.
 13. The compound of claim 8wherein substantially all of the imidazole nitrogens are substitutedwith the RCO— moiety.
 14. The compound of claim 8 wherein the RCO—moiety comprises BrCH₂(CH₂)₃CO—.
 15. The compound of claim 8 exhibitinga solubility in an organic solvent greater than the solubility of thePBI without substitution.
 16. A polymeric medium comprising a PBIcompound having imidazole nitrogens at least 85% of which aresubstituted with a moiety containing a carbonyl group, the substitutedimidazole nitrogens being bonded to carbon of the carbonyl group. 17.The medium of claim 16 comprising a separatory medium.
 18. The medium ofclaim 16 comprising an electronically conductive medium.
 19. The mediumof claim 16 comprising an ionically conductive medium.
 20. The medium ofclaim 16 wherein substantially all of the imidazole nitrogens aresubstituted with the carbonyl-containing moiety.
 21. The medium of claim16 wherein the carbonyl-containing moiety comprises RCO—, where R isorganic and optionally contains an inorganic component.
 22. The mediumof claim 21 wherein R consists of alkoxy or haloalkyl.
 23. The medium ofclaim 16 wherein the carbonyl-containing moiety comprises at least oneof (CH₃)₂CHCH₂OCO—, CH₃CH₂OCO—, and BrCH₂(CH₂)₃CO—.
 24. The medium ofclaim 16 exhibiting a first temperature marking an onset of weight losscorresponding to reversion of the substituted PBI, the first temperaturebeing less than a second temperature marking an onset of decompositionof an otherwise identical PBI compound without the substituted moiety.25. The medium of claim 24 wherein the first temperature is at least 50°C. less than the second temperature.
 26. A polymeric medium comprising aPBI compound having imidazole nitrogens at least a portion of which aresubstituted with a RCO— moiety, where R is organic and optionallycontains an inorganic component, the substituted imidazole nitrogensbeing bonded to the carbon of the RCO— moiety carbonyl group and R beingbonded to the carbon of the carbonyl group by other than a C—O bond. 27.The medium of claim 26 wherein R comprises alkyl, aryl, alkenyl, oralkynyl and the inorganic component comprises oxygen, nitrogen,scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium,molybdenum, tungsten, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, boron, aluminum, gallium, indium, silicon,germanium, tin, phosphorus, arsenic, antimony, sulfur, selenium,tellurium, or oxides thereof.
 28. The medium of claim 26 wherein R isbonded to the carbon of the carbonyl group by a C—C bond.
 29. The mediumof claim 28 wherein R consists of haloalkyl.
 30. The medium of claim 26comprising a separatory medium.
 31. The medium of claim 26 exhibiting anH₂, Ar, N₂, O₂, CH₃, or CO₂ gas permeability greater than the gaspermeability of a comparable separatory medium instead comprising thePBI compound without substitution.
 32. The medium of claim 26 comprisingan electronically conductive medium.
 33. The medium of claim 26comprising an ionically conductive medium.
 34. The medium of claim 26comprising substituted poly-2,2′(m-phenylene)-5,5′-bibenzimidazole. 35.The medium of claim 26 wherein substantially all of the imidazolenitrogens are substituted with the RCO— moiety.
 36. The medium of claim26 wherein the RCO— moiety comprises BrCH₂(CH₂)₃CO—.
 37. A substitutedPBI synthesis method comprising: providing PBI having imidazolenitrogens; reacting the PBI with a compound containing a carbonyl group;and substituting at least 85% of the imidazole nitrogens with a moietyfrom the compound, the substituted imidazole nitrogens being bonded tocarbon of the carbonyl group.
 38. The method of claim 37 wherein the PBIcomprises poly-2,2′(m-phenylene)-5,5′-bibenzimidazole.
 39. The method ofclaim 37 wherein the PBI is provided in a less than 5 wt % solution ofthe PBI in a solvent.
 40. The method of claim 37 further comprisingionizing the imidazole nitrogens before the reacting.
 41. The method ofclaim 40 wherein the ionizing comprises deprotonating with an alkalihydride.
 42. The method of claim 40 wherein the ionizing, reacting, andsubstituting occur at from about 20 to about 30° C.
 43. The method ofclaim 40 wherein the ionizing, reacting, and substituting occur at aboutatmospheric pressure.
 44. The method of claim 37 wherein the reactinguses more than 5 equivalents of the compound in relation to theimidazole nitrogens to be substituted.
 45. The method of claim 37wherein substantially all of the imidazole nitrogens are substitutedwith the moiety.
 46. The method of claim 37 wherein the compoundcomprises RCOX, where R is organic, optionally containing an inorganiccomponent, and X is a leaving group.
 47. The method of claim 46 whereinR comprises alkyl, aryl, alkenyl, or alkynyl and the inorganic componentcomprises oxygen, nitrogen, scandium, yttrium, titanium, zirconium,hafnium, vanadium, niobium, molybdenum, tungsten, iron, ruthenium,cobalt, rhodium, nickel, palladium, platinum, boron, aluminum, gallium,indium, silicon, germanium, tin, phosphorus, arsenic, antimony, sulfur,selenium, tellurium, or oxides thereof.
 48. The method of claim 46wherein R consists of alkoxy or haloalkyl.
 49. The method of claim 46wherein X comprises halogen, cyano, thiocyano, oxycyano, thioalkyl,alkoxy, fluoroalkoxy, sulfonylalkyl, oxyaromatic, thioaromatic,sulfonylaromatic, aromatic and alkyl carbodiimides,N-hydroxysuccinimide, oxyphosphorus containing compounds, or oxysilanecontaining compounds.
 50. The method of claim 37 wherein the compoundcomprises at least one of (CH₃)₂CHCH₂OCOCl, CH₃CH₂OCOCl, andBrCH₂(CH₂)₃COCl.
 51. A substituted PBI synthesis method comprising:providing PBI having imidazole nitrogens; reacting the PBI with a RCOXcompound, where R is organic, optionally containing an inorganiccomponent, and X is a leaving group; and substituting at least a portionof the imidazole nitrogens with a RCO— moiety from the compound, thesubstituted imidazole nitrogens being bonded to the carbon of the RCO—moiety carbonyl group and R being bonded to the carbon of the carbonylgroup by other than a C—O bond.
 52. The method of claim 51 furthercomprising ionizing the imidazole nitrogens before the reacting.
 53. Themethod of claim 52 wherein the ionizing comprises deprotonating with analkali hydride.
 54. The method of claim 51 wherein the reacting usesmore than 5 equivalents of the compound in relation to the imidazolenitrogens to be substituted.
 55. The method of claim 51 whereinsubstantially all of the imidazole nitrogens are substituted with themoiety.
 56. The method of claim 51 wherein R is bonded to the carbon ofthe carbonyl group by a C—C bond.
 57. The method of claim 56 wherein Ris haloalkyl and X is halogen.
 58. The method of claim 51 wherein thecompound comprises BrCH₂(CH₂)₃COCl.
 59. A polymeric medium fabricationmethod comprising: providing PBI having imidazole nitrogens; reactingthe PBI with a compound containing a carbonyl group; substituting atleast 85% of the imidazole nitrogens with a moiety from the compound,the substituted imidazole nitrogens being bonded to carbon of thecarbonyl group; and forming a polymeric medium that comprises thesubstituted PBI.
 60. The method of claim 59 wherein the polymeric mediumcomprises a separatory medium.
 61. The method of claim 60 wherein theseparatory medium exhibits an H₂, Ar, N₂, O₂, CH₃, or CO₂ gaspermeability greater than the gas permeability of a comparableseparatory medium instead comprising the PBI.
 62. The method of claim 59wherein the polymeric medium comprises an electronically conductivemedium.
 63. The method of claim 59 wherein the polymeric mediumcomprises an ionically conductive medium.
 64. The method of claim 59wherein the PBI comprises poly-2,2′(m-phenylene)-5,5′-bibenzimidazole.65. The method of claim 59 further comprising deprotonating theimidazole nitrogens at from about 20 to about 30° C. in a less than 5 wt% solution of the PBI in a solvent.
 66. The method of claim 59 whereinthe reacting and substituting occur at from about 20 to about 30° C. 67.The method of claim 59 wherein the reacting uses at least 10 equivalentsof the compound in relation to the imidazole nitrogens to besubstituted.
 68. The method of claim 59 wherein substantially all of theimidazole nitrogens are substituted with the moiety.
 69. The method ofclaim 59 wherein the compound comprises RCOX, where R is organic,optionally containing an inorganic component, and X is a leaving group.70. The method of claim 69 wherein R comprises alkyl, aryl, alkenyl, oralkynyl and the inorganic component comprises oxygen, nitrogen,scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium,molybdenum, tungsten, iron, ruthenium, cobalt, rhodium, nickel,palladium, platinum, boron, aluminum, gallium, indium, silicon,germanium, tin, phosphorus, arsenic, antimony, sulfur, selenium,tellurium, or oxides thereof.
 71. The method of claim 69 wherein Rconsists of alkoxy or haloalkyl.
 72. The method of claim 69 wherein Xcomprises halogen, cyano, thiocyano, oxycyano, thioalkyl, alkoxy,fluoroalkoxy, sulfonylalkyl, oxyaromatic, thioaromatic,sulfonylaromatic, aromatic and alkyl carbodiimides,N-hydroxysuccinimide, oxyphosphorus containing compounds, or oxysilanecontaining compounds.
 73. The method of claim 59 wherein the compoundcomprises at least one of (CH₃)₂CHCH₂OCOCl, CH₃CH₂OCOCl, andBrCH₂(CH₂)₃COCl.
 74. The method of claim 59 wherein the substituted PBIexhibits a first temperature marking an onset of weight losscorresponding to reversion of the substituted PBI, the first temperaturebeing less than a second temperature marking an onset of decompositionof an otherwise identical PBI compound without the substituted moiety,and forming the polymeric medium comprises heating treating thepolymeric medium and removing the substituted moiety from the PBI.
 75. Apolymeric medium fabrication method comprising: providing PBI havingimidazole nitrogens; reacting the PBI with a RCOX compound, where R isorganic, optionally containing an inorganic component, and X is aleaving group; substituting at least a portion of the imidazolenitrogens with a RCO— moiety from the compound, the substitutedimidazole nitrogens being bonded to carbon of the RCO— moiety carbonylgroup and R being bonded to the carbon of the carbonyl group by otherthan a C—O bond; and forming a polymeric medium that comprises thesubstituted PBI.
 76. The method of claim 75 wherein the polymeric mediumcomprises a separatory medium.
 77. The method of claim 75 wherein thepolymeric medium comprises an electronically conductive medium.
 78. Themethod of claim 75 wherein the polymeric medium comprises an ionicallyconductive medium.
 79. The method of claim 75 further comprisingdeprotonating the imidazole nitrogens at from about 20 to about 30° C.in a less than 5 wt % solution of the PBI in a solvent.
 80. The methodof claim 75 wherein the reacting uses at least 10 equivalents of thecompound in relation to the imidazole nitrogens to be substituted. 81.The method of claim 75 wherein substantially all of the imidazolenitrogens are substituted with the RCO— moiety.
 82. The method of claim75 wherein R is bonded to the carbon of the carbonyl group by a C—Cbond.
 83. The method of claim 82 wherein R is haloalkyl and X ishalogen.
 84. The method of claim 75 wherein the compound comprisesBrCH₂(CH₂)₃COCl.